Temperature- and doping-dependent roles of valleys in the thermoelectric performance of SnSe: A first-principles study

Abstract

We theoretically investigate how each orbital and valley play a role in high thermoelectric performance of SnSe. In the hole-doped regime, two kinds of valence band valleys contribute to its transport properties: one is the valley near the U-Z line, mainly consisting of the Se-${p}_{z}$ orbitals, and the other is the one along the $\mathrm{\ensuremath{\Gamma}}$-Y line, mainly consisting of the Se-${p}_{y}$ orbitals. Whereas the former valley plays a major role in determining the transport properties at room temperature, the latter one also offers comparable contribution and so the band structure exhibits multivalley character by increasing the temperature. In the electron-doped regime, the conduction band valley around the $\mathrm{\ensuremath{\Gamma}}$ point solely contributes to the thermoelectric performance, where the quasi-one-dimensional electronic structure along the $a$ axis is crucial. This study provides important knowledge for the thermoelectric properties of SnSe, and will be useful for future searches for high-performance thermoelectric materials.